You're speaking with Dr. Michael Salkin. Welcome to JustAnswer. I'm currently typing up my reply.
How old is your kitten please? There's no direct relationship between eating a lot of mice and struggling to walk but I would be concerned if he ingested a mouse poisoned by an anticogulant rodenticide. Cats that do so can then begin bleeding uncontrollably from any body orifice or internally leading to profound anemia and weakness which might be indicated by "struggling to walk". Please check your kitten's gums and tongue. They should be nicely pink - not whitish (anemia). Please let me know what you find.